This invention relates to automatic assembly equipment and, in particular, to the automatic assembly of semiconductor devices.
In the past various mechanisms have been used to automatically select a chip from a wafer and transport the chip to a bonding site. Typically an arm comprising a capillary is used to lift the chip by maintaining a slight vacuum in the capillary. While early designs were sufficient to automate, or partially automate, the assembly process, several problems arise as one tries to increase the speed of the equipment. For example, picking a die from a wafer is difficult to do quickly without damaging the die. Typically, a die is selected and held by a capillary or hollow tube or needle having reduced pressure therein, using ambient pressure to hold the die against the end of the capillary. In order to increase the speed at which the die is picked up, one cannot arbitrarily increase the vacuum, i.e. decrease the absolute pressure, in the capillary since at least the surface of the chip will be damaged by contact with the capillary. Worse, the chip can crack under the strain imposed by the capillary.
At the bond site, the die must not only be accurately placed on the lead frame, it must not be placed so heavily as to cause damage. Conversely, it has been found that bonding is erratic if the die are placed too lightly on the lead frame.
Another problem with prior art devices is that the high temperature required at the bond site for certain bonding processes deteriorates the operation of the die pick head. It has been found that the lubricants used deteriorate with temperature such that the capillary cannot move freely within the head, or at least not quickly enough for the assembly rates desired, e.g. greater than four thousand bonds per hour.